The device relates to a method for roasting and for the surface pasteurization of pieces of food products, in particular oleaginous seeds, such as almonds, hazelnuts, pecans, walnuts, as well as peanuts, bran, cereals, coffee, cocoa and the like. By nature, agricultural products and foods are loaded with harmless and potentially pathogenic micro-organisms. In most cases, agricultural products are processed fresh, or are made durable with the aid of suitable technological means. Among industrially employed preservation methods are, inter alia, sterilization or pasteurization by means of heat, irradiation with ionizing rays, and gassing with lethally-acting gases. The two last-mentioned methods in particular can only be employed in a limited manner, since the use of these methods is strictly regulated by law.
In the past years, several cases of contamination of raw almonds with salmonella have been reported. To improve the safety of almond products, U.S. authorities have ordered that, starting in autumn of 2007, the entire almond harvest is to be pasteurized. Pasteurization of almonds and other oleaginous seeds requires special demands on the methods to be used. The water content of the almonds is not allowed to be increased to an appreciable degree, by and during treatment, because both the storage capability and the integrity of the almonds are harmed. Moreover, in the course of intensive thermal or mechanical treatment, raw almonds tend to lose the skin around the seed, decreasing quality.
Moreover, US authorities have made the requirement that pasteurization may take place within the course of the customary subsequent processing steps, such as, for example, during blanching or roasting. Here, sufficient inactivation must be assured by the sum of these process steps.
Various devices and methods have been described for hot-air roasting of nuts and almonds. A compilation of these methods can be found in Finke (1965), Kleinert (1966), Gaupp (1978), Bockelmann (1987) or Perren (1995). Commonly, in hot-air roasting methods, the nuts are charged with dry, hot air at 125° C. to approximately 600° C. Because of this, the nuts are heated and are roasted within 8 to 60 minutes. Roasting is characterized by the formation of a roasting stage. By roasting, the water content is reduced to less than 2.5%, and the texture is modified to a crunchy-crackly and brittle texture. Furthermore, a roast color is formed in the range between light brown to dark brown, and a typical roasting aroma and pleasant roasted taste are created.
Effective heat inactivation of micro-organisms is customarily obtained in an atmosphere of increased water activity. In contrast thereto, micro-organisms are only inactivated to a limited extent by dry heating. Since roasting by means of hot air constitutes treatment in a dry atmosphere, an assured inactivation of micro-organisms by hot-air roasting only takes place after a very long treatment time, or respectively at high temperatures.
Parameters which are required for achieving inactivation of the described surrogates for Salmonella SE PT 30 at an order of a magnitude of 4 log-units, are described in the “Guidelines for Validation of Dry Roast Processes” of the Almond Board of California. The described product temperature, time, and/or combinations thereof, which must be attained for minimal heat inactivation in the course of hot-air roasting, are so high that at these conditions high roasting stages and correspondingly dark roast colors are exclusively formed. Thus, only in the case of very advanced roasting stages is it possible to achieve an inactivation of micro-organisms in an order of a magnitude of 4 log-units which, in accordance with the stipulation of the American authorities, does not permit a classification of “pasteurized”.
In the two-stage roasting process of Perren et al. (1996), the hot air is subjected to moisturizing, which leads to an increase in atmospheric humidity. The described increase in humidity in the first process stage to approximately 10% is not sufficient here for creating an atmosphere which causes the assured inactivation of vegetative micro-organisms.
On the other hand, methods for sterilizing pieces of food, and in particular of almonds, have been described. A compilation of the methods accepted for pasteurizing almonds is provided on the website of the Almond Board of California (www.almondsarein.com).
Many described pasteurization methods deal with isolated treatment of products in humid atmospheres at temperatures in the range of 60 to 100° C. under normal pressure conditions. The exclusive aim of these methods is to reduce the contamination of the surfaces of the almonds by micro-organisms. Because of the short process duration and because of the humid atmosphere, these methods are not capable of forming a roasting stage. Neither is drying of the products to <2.5% achieved, nor are there typical textures, roasting aromas and roast colors with these pasteurization methods.
Thus, no method is described in the prior art capable of pasteurizing nuts, almonds, oleaginous seeds and other goods in piece form, simultaneously or in the same process, in an assured manner, and to roast them in hot air.
It is the object of the invention to create a method of the type described at the outset, wherein hot-air roasting and pasteurization of food products are combined and both methods are united.
In accordance with the invention, this object is attained in that a treatment in a humid atmosphere is performed at a temperature <100° C., that pasteurization is performed in a roasting system during the roasting process, that during the pasteurization phase the temperature on the product surface is maintained a few degrees below the selected dew-point temperature of the atmosphere, that pasteurization is performed within 1 to 30 mins, and that, in the course of advancing or continued roasting, condensation water on the surface of the food products is removed and water absorption of the latter is minimized.
Conditions are created for inactivating vegetative germs under optimal conditions and in a short time. The roasting process is subsequently continued and the products are brought to the desired degree of roasting.
Pasteurization is optimized in that the treatment is performed in a humid atmosphere, preferably at temperatures between 50° C. and 90° C., and during the pasteurization phase the temperature on the product surface is preferably selected to lie 0° C. to 8° C. below the dew-point temperature selected for the atmosphere.